It is known to calibrate a fuel injector's dynamic flow by selectively setting the degree of compression of a spring that acts on the armature. This is because the dynamic flow is a function of the response time of the fuel injector, and the response time of the fuel injector is in turn a function of the degree of spring compression. In a top-feed type fuel injector, such calibration is accomplished by using a hollow tube to compress the spring while the flow is being measured, and then staking the tube in place after the desired flow has been attained. The use of a hollow tube allows the liquid fuel to be fed through the means of adjustment and does not require any sort of fluidic seal. A bottom-feed type fuel injector is dynamically calibrated by using a solid adjusting pin to compress the spring, but a fluid seal is required to contain the fuel since the fuel inlet to the fuel injector is located closely adjacent the fuel outlet from the fuel injector.
In many automotive vehicles, the increasing scarcity of available space within the engine compartment has created a demand for miniaturized fuel injectors. The ability to decrease the size of a top-feed fuel injector is limited by the requirement that the size of the fuel hole through the adjusting tube be large enough to accommodate the maximum fuel flow without imposing an unacceptable restriction to that flow. While a bottom-feed fuel injector that is dynamically calibrated in the manner described above requires no fuel hole through the adjusting pin, it is necessary that a sealing means be provided around the calibration means. Such a sealing means occupies space and therefore inhibits the ability to miniaturize that type of fuel injector.
Commonly assigned co-pending application Ser. No. 07/738,653 filed Jul. 31, 1991 now U.S. Pat. No. 5,517,967 discloses an invention which attains a desired dynamic flow calibration by the creation of a desired condition for the forces acting on the fuel injector's armature. This is accomplished by the selective relative positioning of the injector's stator/armature interface to the injector's solenoid coil. Two specific advantages of the invention that allow for fuel injector miniaturization include the elimination of the need for a fluid sealing means around the means which selectively sets the dynamic calibration, and the ability to perform the dynamic calibration in a very small amount of space. Increased resolution within the calibration range is yet another advantage.
Like the invention of Ser. No. 07/738,653, the present invention relates to a new and improved method for dynamic flow calibration of an electromagnetically operated fuel injector which renders the fuel injector more conducive to miniaturization. The invention also relates to a novel construction for an electromagnetically operated fuel injector that promotes the efficient practice of the method, particularly in the automated mass-production fabrication of such fuel injectors.
Briefly, the present invention relates to a fuel injector in which a control rod is positioned in relation to the stator and armature during dynamic flow calibration to selectively divert some of the magnetic flux from the working gap by causing the diverted magnetic flux to pass directly between the stator and the armature without passing through the working gap. The fuel injector also includes a non-magnetic tube disposed between the control rod and holes in the stator and armature through which the control rod passes. The portion of that tube which is within the stator hole is joined to the stator while the portion which is within the armature hole provides guidance for the armature. In a bottom-feed version of the fuel injector, the tube serves to prevent fuel within the injector from wetting the control rod. The fuel injector is dynamically calibrated by selectively positioning the control rod by means of an external tool that engages the control rod.
The foregoing, along with additional features, advantages, and benefits of the invention will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at the present time in carrying out the invention.